The present invention relates to a medium transport device and an image forming apparatus.
In a conventional image forming apparatus such as a printer, a copier, a fax machine, and a multifunction machine thereof, an image forming unit forms a toner image according to print data, and a transfer unit transfers the toner image to a sheet as a medium. Then, the sheet is transported to a fixing device, thereby fixing the toner image. Afterward, the sheet is discharged to a specific location with a pair of transport rollers.
In the conventional image forming apparatus such as a printer, a sheet cassette is detachably attached to an apparatus main body of the printer for storing the sheet. In the sheet cassette, a medium placing base is rotatably disposed on a support shaft for placing the sheet. Further, in the sheet cassette, a medium regulating member is disposed for regulating a position where the sheet is placed, so that the medium regulating member positions the sheet in a direction that the sheet is transported and a direction perpendicular to the direction that the sheet is transported.
Further, the conventional image forming apparatus is provided with a sheet supply roller; a separation member facing the sheet supply roller; and a pressing member pressing the separation member, so that the sheet is supplied from the sheet cassette. A guide member formed of a base portion and a plurality of rib portions is disposed at a downstream side of the sheet supply roller for supplying the sheet. The rib portions have an identical shape. A pair of the transport rollers is disposed at a downstream side of the guide member.
When a sheet supply motor drives the sheet supply roller to rotate at a constant speed, the sheet is picked up from the medium placing base. Then, the sheet is transported to a nip portion between the sheet supply roller and the separation member to be separated one by one, and is transported to the guide member. Accordingly, the sheet passes through a medium sensor while abutting against the rib portions of the guide member, and is transported to a pair of the transport rollers.
A control unit controls the transport rollers to rotate for transporting the sheet according to a timing when the sheet passes through the medium sensor. In general, the control unit controls the transport rollers not to start rotating for a specific period of time after the sheet passes through the medium sensor, so that the sheet is pushed into the transport rollers to correct skew thereof (refer to Patent Reference). Patent Reference Japan Patent Publication No. 10-171199
In the conventional printer, when a front edge of the sheet is caught with a distal end of the rib portion and bent, a transport jam may occur.
In the view of the problem described above, an object of the present invention is to provide a medium transport device and an image forming apparatus capable of solving the problem and preventing a transport jam of a sheet.
Further objects and advantages of the invention will be apparent from the following description of the invention.